The invention relates to a tensioner for a power transmission belt.
Tensioners for belt power transmission systems have already been proposed, in particular by the Applicant in FR-A-2 597 565 or FR-A-2 612 591. In the embodiments according to these documents, a linear tensioner for a power transmission belt comprises a return spring associated with the shaft of a tensioner roller with which the belt cooperates for controlling the displacement of said roller and the action of said spring, which is coated with elastomer forming a sheath defining at least a variable volume chamber filled with a liquid, said chamber being closed at one of its ends by a valve device, through which the passage of the liquid entering or leaving said chamber introduces an effect of damping the vibrations likely to occur in the belt. Although devices of this type are satisfactory for obtaining the desired results, it has proved that their construction, in particular in so far as the manufacture of the elastomer sheaths and fixing them at their ends are concerned, lead to manufacturing costs which are too high for devices for used in the automobile industry where the price factor is of great importance.
In other documents, for example in FR-A-2 617 556, also in the name of the Applicant, a tensioner of rotary type is described having a helical spring exerting a resilient return torque and comprising a flexible member of a general toroidal shape divided into two fluid chambers separated at one of their ends by a valve with dissymmetric operation so as to introduce the desired damping effect. The manufacture of such a device is also relatively expensive and leads to a relatively cumbersome assembly.
Since, however, the natural extension of the belt during use, as well as the vibrations generated in the belt by cyclic irregularities of the engine speed, are accompanied by slipping of the belt over the pulleys of the driven members--with consequently transmission defects--it is important to remedy this drawback of belt power transmissions using a tensioner, either rotary or linear depending on the organization of the belt power transmission, but which in all cases must be of as low a size and cost as possible, while offering great safety and reliability.